In this century, machines have come to be widely used for washing articles of clothing. These machines typically run through an automatic sequence of washing, rinsing, and spin-drying steps alternatingly receiving and discharging water with each step. The discharged "grey" water, including contaminating detergents and suspended particulate matter, is most often conveyed through the drainage system of a building structure into a public sewer line for ultimate disposal. In some instances, however, blockages in such drainage systems have lead to large volumes of grey water being discharged onto the floor of a building structure and causing considerable damage thereto.
In my prior patent, U.S. Pat. No. 4,069,837, issued Jan. 24, 1978, a device for detecting a blockage in a drainage system and preventing a damaging overflow condition by disabling a washing machine was disclosed. In order to function as intended, the device illustrated in my patent required a readily-achieved, fluid-tight seal with the stand-pipe or inlet to the drainage system of a building structure. While my original device was fully effective in accomplishing its principal intended purpose, i.e., preventing unintended spillage, the pressurized back-flow of fluid through the stand-pipe or drainage system inlet was found not to be substantially deterred from reentering a washing machine after its initial discharge.
In highrise apartments and washaterias, where multiple clothes washing machines discharge grey water into a common drainage system, the potential for fluid back-flow is especially acute. As a single washing machine is discharging its liquid contents under pressure, a downstream blockage can lead to the undesired entry of the just pumped grey water into several other machines and contamination of the contents thereof.